Nowadays, thermosensitive printing devices are widely used in catering industries, retail industries, equipment management fields, transportation fields, and so on. The thermosensitive printing devices can be used to print transaction certificates, equipment labels and transport numbers. As the applications of the thermosensitive printing devices are gradually expanded, the types of the print media to be used are diversified. Generally, the pressure of the printhead module of the thermosensitive printing device is correlated with the thickness, the width and the sensed temperature of the print medium. In other words, the pressure of the printhead module for a different print medium is different. Since the pressure of the printhead module has a high influence on the printing quality, the conventional thermosensitive printing device is usually equipped with a pressure adjusting mechanism for adjusting the pressure on the printhead module. The pressure adjusting mechanism has a spring structure. By using the pressure adjusting mechanism, the pressure value is maintained in the optimized pressure range. Consequently, the thermosensitive printing device has the better printing quality.
FIG. 1 is a schematic cross-sectional view illustrating the structure of a conventional printhead pressure adjusting mechanism. The conventional printhead pressure adjusting mechanism is disclosed in Chinese Patent Publication No. CN201120569726.9. As shown in FIG. 1, the printhead pressure adjusting mechanism 1 comprises a supporting shaft 16 and two pressure adjusting assemblies 17. The two pressure adjusting assemblies 17 are separated from each other and fixed on the supporting shaft 16. Each pressure adjusting assembly 17 comprises a bracket 11 and a movable post 14. The bracket 11 is fixedly connected with the supporting shaft 16. The movable post 14 comprises a thread structure and an adjusting nut 13 corresponding to the thread structure. A first end of the movable post 14 has the thread structure. Moreover, the first end of the movable post 14 is penetrated through an opening (not shown) of the supporting shaft 16. A second end of the movable post 14 has a movable block 15. The movable block 15 is contacted with a printhead module (not shown). Moreover, a spring 12 is sheathed around the movable post 14 and arranged between the supporting shaft 16 and the adjusting nut 13. A print medium (not shown) is transferred through the region between the printhead module and a print roller (not shown). Moreover, the print medium is pressed by the printhead module.
As the adjusting nut 13 of the printhead pressure adjusting mechanism 1 is rotated, the deformation amount of the spring 12 is changed. Consequently, the pressure of the movable block 15 applied to the printhead module is adjusted.
However, the printhead pressure adjusting mechanism 1 still has the following drawbacks. Firstly, in case that a side of the print medium is aligned with a side of the width of the printhead module (i.e., in a side-by-side arrangement) and the width of the print medium is small (i.e., a narrow print medium), there is a gap between the print roll and the region without the print medium. Under this circumstance, the printhead module is inclined along the width of the print medium. For assuring the printing quality and correcting the inclined printhead module, it is necessary to increase the printhead pressure on the print medium. Although the increase of the printhead pressure results in reliable contact between the printhead module and the print medium, the possibility of causing damage of the printhead module increased. Moreover, the force of the printhead module is also not uniformly exerted on the printhead medium.
Secondly, the rotation of the adjusting nut 13 changes the deformation amount of the spring 12, and thus the pressure of the movable block 15 applied to the printhead module is correspondingly changed. Generally, the adjusting nut 13 is located at a lateral side of the pressure adjusting assembly 17. Since the printhead pressure adjusting mechanism 1 is covered by a casing (not shown) of a thermosensitive printing device (not shown), it is not convenient for the user to rotate the adjusting nut 13. For example, the casing has to be detached from the thermosensitive printing device when the process of rotating the adjusting nut 13 is performed.
Thirdly, during the process of using the thermosensitive printing device, it is not easy for the user to recognize the status of the adjusting nut 13 and the rotation amount of the adjusting nut 13. If the type of the print medium is changed, the user cannot quickly rotate the adjusting nut 13 to a proper position to have the printhead module apply a suitable pressure on the print medium.
In other words, the conventional thermosensitive printing device needs to be further improved.